it is very unlikely that intellectual needs will be met in school
There is a lot of truth in the above statement. For HG+ kids, even a 2-3 year acceleration in the areas that they are strong in is not challenging enough. I have yet to see a school that can keep up with a highly capable child's academic needs.
Math is one of the subjects for which there are unlimited resources available to study independently - he can easily be on his own track either with an online course like AOPS or with a tutor. So, take that into consideration when evaluating the options.
I have a child who would be crushed if he could not play basketball with his friends at recess time. His social bonding comes through shared experiences with friends involving sports and it is very crucial to his happiness and lack of anxiety at school.
